The accumulation of several toxic elements, such as lead, within human beings can cause significant, serious health problems. For example, the accumulation of lead within children can lead to a variety of behavioral and educational disabilities. To determine whether metal toxicity is the cause of such problems, it is desirable to have a simple and sensitive method for measuring the levels of an element in the blood or extracting an element, such as lead from blood. Such a method would also enable physicians to monitor the efficacy of treatments for reducing the deleterious accumulation of this metal in the body.